Controlled electron buncher



May 3, 1966 Filed April 2, 1964 F. E. WELKER ETAL CONTROLLED ELECTRON BUNCHER 5 Sheets-Sheet l May 3, 1966 Filed April 2, 1964 F. E. WELKER ETAL 3,249,793

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United States Patent O 3,249,793 CNTROLLED ELECTRON BUNCHER Frank E. Welker and William C. Quinn, Rome, N.Y., assignors to the United States of America as represented by the Secretary of the Air Force Fiied Apr. 2, 1964, Ser. No. 356,994 8 Claims. (Cl. 315-5) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to us of any royalty thereon. I

This invention relates, in general, to electron tubes, and in particular, to la controlled electron buncher capable of producing an output of extremely short pulses.

Extremely short pulses, of nanosecond duration, are required for future development of high resolution radar systems. Now, it is well known that the conventional technique of applying a video pulse to an electron gun becomes increasingly more diicult as the pulse width is shortened. At nanosecond pulse widths, lead induct-ance and interelectrode capacity present very diicult, in most The invention herein, all but eliminates the eifects of lead inductance and interelectrode capacity by forming yand isolating electron bunches prior topulsing. i

Therefore, it is an object of this invention to provide a controlled electron buncher for a vacuum tube.

`It is another object of this invention to provide an electron buncher device capable of producing an output of nanosecond pulse widths.

A further object is the formation and isolation of electron bunches in `a trapping region and a subsequent dumping thereof by application of a suitable signal to produce an output of nanosecond pulse width.

It is still another object of the invention to provide a controlled electron buncher which is economical to produce and which utilizes conventional, currently available components that lend themselves to standard mass production manufacturing techniques.

Other lobjects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

FIGURE l is a schematic representation of the invented device;

`FIGURE 2 is la schematic representation of the inventions electrode conguration with a series of electric potential distribution curves directly therebelow;

FIGURE 3 is an alternate operation for the schematic representation of FIGURE 2; and

FIGURE 4 is a schematic representation of an alternate electrode geometry.

With reference to the figures, wherein like numerals refer to like parts, the electron source 10, the post-accelerator 20', and the trapping region 30, are the three major regi-ons of the device which are generally arranged along an axis Z as shown in -FIGURE l. It is understood, of course, that the electrode geometry may take many alternate forms, however, `the underlying principles of operation will, in all cases, be the same.

The electron source 10 may be any cathode or other suitable electron supplier which is capable of supplying the desired current level to the trapping region. A conventional electron gun of the cathode ray type may be utilized to provi-de a suitable and well defined beam of electrons.

The post-accelerator 20 may be any appropriate conventional electr-ode or electrodes which upon application of suitable voltage will accelerate electrons to a desired translational energy, for example, a flat disk, or a more complicated wide band coaxial interaction structure.

ICC

The acceleration electrode is maintained at a high positive potential.

The trapping region 30 is the heart of the invented device wherein electron bunches are formed, isolated and then dumped to the post-accelerator 20. During the trapping interval, the potential distribution along the trapping region is such that it prevents electrons entering therein from either advancing to the post-accelerator 20, or returning to the source 10. Advancement to the postaccelerator 20 is prevented by establishing a negative potential, with respect to the 4midportion 36 of trapping region 30, at a portion 34 thereof proximate to accelerator 20. This potential dilerence must be greater than the combined kinetic and potential energies of the trapped electrons throughout the interval. Return to the electron source 10 is prevented by continually increasing the potential difference between the electron source 10 and midpoint 36 of the trapping region 30, throughout the trapping interval. 'In this manner, electrons leaving source 10 and entering trapping region 30 will always encounter a greater potential difference if they attempt to return to source 10 :at some later time. Essentially, the aforedescribed trapping technique may be considered at a time varying potential well for electrons. Radial confinement of electrons may be accomplished by a magnetic field parallel to the Z axis by any conventional means such as by a solenoid or permanent magnet as illustrated in FIGURE 4. The electric potential distribution may be established by conventional electron tube techniques, well known in the art.

Isolation of an electron bunch in the trapping region 30 may be accomplished by -applying a pinch-01T pulse at the portion 32 of trapping region 30 which is proximate to source 10. The pinch-off pulse establishes a negative potential with respect to source 10 for an instantaneous isolation of Ian electron bunch from source 10.

Dumping of the trapped `and isolated electron bunch may then be easily accomplished by changing the potential distribution in trapping region 30 so the electron bunch therein are forced out toward the accelenator 20.-

The different portions of trapping region 30 may be dened by individual electrodes, as illustrated in FIG- URES 2 and 3. Pinch-oit electrode 32 may be a short cylindrical can with a small axial hole therethrough. As shown, pinch-olf electrode 32 is mounted proximate the cathode gun 10. A barrier electrode 34 is provided proximate the accelerator electrode 20. Barrier electrode 34 may be ashort open cylinder. A storage electrode 36 formed by an open cylinder, is provided between the pinch-off electrode 32 and barrier electrode 34, as shown.

FIGURE 4 illustrates an alternate electrode configuration which gives the same electric potential distribution of FIGURES 2 and 3 for the trapping region 30. A helix of resistive wire which is tapped at appropriate points may be utilized as a single trapping region electrode. In this instance, pinch-off, storage, and barrier taps 32, 36, 34 are provided in place of the pinch-olf, storage, and barrier electrodes 32, 36, 34, respectively. The helix conguration is of special interest because the helix may be utilized as aslow wave matched transmission line as shown in FIGURE 4 with a termination RL. Thus, during dumping, the trapped electron bunch in the potential well 36 of trapping region 30 would be forced by the pulse leading edge toward the acceleration electrode 20.

Operation of the device may be better understood by reference to the potential distribution curves of FIGURES 2 and 3. The curves A, B, C, D, indicate potential distribution along the Z axis at time intervals throughout the trapping, isolating and dumping procedures. Notice that the potential axis has been inverted in order that the barriersfand wells will appear as such in the gravitational sense for the negative electron. The trapping interval or storage cycle begins with the potential distribution shown in curve A of FIGURE 2. At curves B and C the potential well deepens through the application of a positive ramp to the storage electrode 36,which technique, explained beforehand, prevents electrons therein from advancing or returning. At curve C a pluse is applied to the pinch-off electrode 32 establishing it with a highly negative potential with respect to the cathode gun at the instant that electron bunch formation is halted. This accomplishes an instantaneous isolation of the completely formed potential well from the cathode 10. At curve D the storage electrode 36 has been pulsed negatively, changing the potential distribution to dump the electron bunch towards the acceleration electrode 20. Dumping may be facilitated by a positive pulsing (dashed line) of the barrier electrode 34 simultaneous with the negative pulsing of storage electrode 36, as represented by the dashed curve E.

FIGURE 3 is an alternate operation, wherein the storage electrode 36, and barrier electrode 34 sustain xed potentials throughout the trapping interval. At A and B, FIGURE 3, the cathode gun V1t) and pinch-off electrode 32 are made progressively negative throughout the trapping interval. At C, an instant before the cathode 10 reaches the potential of barrier electrode 34, the pinch-off electrode 32 is pulsed to a high negative potential to isolate the cathode 10 from the trapping region 30. At D, dumping proceeds in the same manner as explained in FIGURE 2.

Although the invention has been described with reference to a particular embodiment, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claims.

We claim:

1. A vacuum tube device for forming, isolating, and accelerating controlled electron bunches, comprising: an electron source; an electron post-accelerator having a high positive potential with respect to said source; an electron trapping region disposed between said source and accelerator; means for applying a potential distribution along said trapping region which prevents electrons entering therein from advancing and returning, respectively, to said accelerator and source, thereby forming an electron bunch therein; means to apply a pinch-off pulse at a portion of said trapping lregion proximate said source, said pulse establishing a negative potential with respect to said source for an instantaneous isolation therefrom of said electron bunch; and means to apply a dumping pulse subsequent to said isolation, said dumping pulse changing said potential distribution along said trapping region to force said electron bunch toward said post-accelerator for acceleration therefrom producing a pulsed output.

2. A vacuum tube device for forming, isolating, and accelerating controlled electron bunches, comprising: an electron source; an electron post-accelerator having a high positive potential, with respect to said source, which is suitable to accelerate electrons to a desired translational energy; an electron trapping region disposed between said source and accelerator; means for applying a potential distribution along said trapping region which has, in respect to midportion thereof, a negative potential proximate said accelerator and a continually increasing potential difference from said source, said distribution, respectively, preventing electrons entering therein from advancing and returning to said accelerator and source, thereby forming an electron bunch therein; means to apply a pinch-oi pulse at a portion of said trapping region proximate said source, said pulse establishing a negative potential with respect to said source for an instantaneous isolation therefrom of said electron bunch; and means to apply a dumping pulse to said region, subsequent to said isolation, said dumping pulse changing said potential dis- .tribution along said trapping region to force said electron bunch toward said post-accelerator for acceleration therefrom producing a pulsed output.

3. A vacuum tube device for forming, isolating, and accelerating controlled electron bunches, comprising: an electron source; an electron post-accelerator having a -high positive potential, with respect to said source, which is suitable to accelerate electrons to a `desired translational energy; an electron trapping region disposed between said source and accelerator, lsaid trapping region including a pinch-od portion proximate said source, a storage portion midway therealong, and a barrier portion proximate said accelerator; means for applying a potential distribution along said trapping region which has, in respect to said storage portion, a negative potential at said barrier portion and a continually increasing potential difference from said source, said distribution, respectively, preventing electrons entering therein from advancing and returning to said accelerator and source, thereby forming an elec-tron bunch therein; means to .apply a pulse yat saidv pinch-off portion, said pulse establishing a negative potential with respect to said source for an instantaneous isolation therefrom of said electron bunch; and means to apply a dumping pulse at said Stor-age portion subsequent to said isolation, said dumping pulse changing said Ipotential distribution along said trapping region to force said electron bunch toward said post-accelerator for acceleration therefrom producing a pulsed output.

4. A vacuum tube device for forming, isolating, and accelerating controlled electron bunches, comprising: an electron source; an electron post-accelerator having a high positive potential, with respect to said source, which is suitable to accelerate electrons to a desired translational energy; an electron trapping region disposed between said sour-ce and accelerator, said trapping region including a pinch-off portion proximate said source, a storage portion midway there-along, and a barrier portion proximate said accelerator; means for applying a potential distribution al-ong said trapping region which has, in respect to said storage portion, a negative potential at said barrier portion and a continually increasing potential diiference from said source, said distribution, respectively, preventing electrons entering therein from advancing and returning to said accelerator and source, thereby forming an electron bunch therein; means to apply a pulse `at said pinch-off portion, said pulse establishing a negative potential with respect to said source for an instantaneous isolation therefrom of said electron bunch; means to apply a negative dumping pulse at said storage portion subsequent to said isolation; and means to apply a positive pulse at said barrier portion simultaneously with said dumping pulse thereby changing said potential distribution along said trapping region to force said electron bunch toward said postaccelerator for acceleration therefrom producing a pulsed output.

5. A vacuum tube device for forming, isolating, and accelerating -controlled electron bunches, comprising: an electron gun of the cathode ray type providing a well dened beam of electrons; a post-acceleration electrode having a high positive potential with respect to said gun, which is suitable to accelerate electrons toa desired translational energy; an electron trapping region disposed between said gun and acceleration electrode, said region defined by a pinch-'off electrode proximate :said gun, a barrier electrode proximate said accelerator electrode, with a storage electrode therebetween; means for applying a potential distribution along said trapping region which has, in respect to said storage electrode, a negative potential .at said barrier electrode `and a continually increasing potential difference from said gun, said distribution, respectively, preventing electrons entering therein from advancing and returning to said accelerator electrode and gun, thereby forming an electron bunch therein; means to apply a pulse at said pinch-off electrode, said pulse establishing a negative potential with respect to said gun for lan instantaneous isolation therefrom of said electron bunch; and means to apply a negative dumping pulse at said storage electrode subsequent to said isolation, said dumping pulse changing said potential distribution along said trapping region to force said electron bunch toward said post-accelerator electr-ode for acceleration therefrom producing a pulsed output.

`6. A vacuum tube 4device for forming, isolating, and yaccelerating controlled electron bunches by application of a suitable signal to pro-duce an output of nanosecond pulse Width capabilities, comprising: an electron gun of the cathode ray type providing a well defined beam of electrons; a post-acceleration electrode having 'a wide band coaxial inter-action structure -at a high positive potential with respect to said gun, and which is suitable to accelerate electrons to a desired translational energy; an electron trapping region disposed between said gun and acceleration electrode, said region having, proximate said gun a pinch-off electrode formed of a short cylindrical can with an axial hole therethrough, proximate said acceleration electrode a short open cylindrical barrier electrode, and an open cylindrical storage electrode between said pincholf and barrier electrodes; means for applying a potential distribution along said trapping region which has, in respect to said storage electrode, a negative potential at said barrier electrode, and `a continually increasing potential difference from said gun, said distribution, respectively, preventing electrons entering therein from advancing and returning to said accelerator electrode and gun, thereby forming an electronbunch therein; means to provide a :strong magnetic field paralleling said beam of electrons to accomplish radial connernent thereof; means to apply a pulse at said pinch-off electrode, said pulse establishing a negative potential with respect t-o said gun for an instantaneous isolation therefrom of said electron bunch; means to apply a negative dumping pulse at said storage electrode subsequent to said isolation; and means to apply a positive pulse fat said barrier portion simultaneously with said dumping pulse thereby changing said potential distribution along said trapping region to force said electron bunch toward said post-accelerator for acceleration therefrom, said bunches being suitable to produce an output of nanosecond pulse Width.

7. A combination as claimed in claim 6 wherein said storage electrode comprises a helix wound Wire, said helix `affording a slow wave, matched transmission line wherein with respect to said gun, and which is suitable to accelerate electrons to a desired translational energy; an electron 4trapping region disposed between said gun and acceleration electrode, said region deued by a helix of resistive Wire, with a pinch-off tap proximate said gun, a barrier tap proximate said :acceleration electrode, ya storage tap midway therebetween, and a dumping tap between said pinch-01T and storage taps; means for applying a potential distribution al-ong said trapping region which has, in respect to said storage tap, a negative potential at said barrier tap, and a continually increasing potential difference from said gun, said distribution respectively, preventing electrons entering therein from advancing and returning to said acceleration electrode and gun, thereby forming an electron bunch therein; means to provide a strong magnetic iield paralleling said beam of electrons to accomplish radial confinement thereof; means to apply a' pulse at said pinch-off'tap, said pulse establishing a negative potential with respect to said gun for an instantaneous isolation therefrom of said electron bunch; and means to apply a negative dumping pulse at said dumping tap subsequent to said isolation, said lhelix atiording a slow wave matched transmission line with lan advancing edge of said dumping pulse forcing said electron bunch toward said post-acceleration electrode for acceleration therefrom, said bunches lbeing suitable to produce an output of nanosecond pulse width.

References Cited by the Examiner UNITED STATES PATENTS 2,232,050 2/1941 Clavier S15-6.34 X

DAVID I. GALVIN, Primary Examiner. ROBERT SEGAL, Examiner. S. D. SCHLOSSER, Assistant Examiner, 

4. A VACUUM TUBE DEVICE FOR FORMING, ISOLATING, AND ACCELERATING CONTROLLED ELECTRON BUNCHES, COMPRISING: AN ELECTRON SOURCE; AN ELECTRON POST-ACCELERATOR HAVING A HIGH POSITIVE POTENTIAL, WITH RESPECT TO SAID SOURCE, WHICH IS SUITABLE TO ACCELERATE ELECTRONS TO A DESIRED TRANSLATIONAL ENERGY; AN ELECTRON TRAPPING REGION DISPOSED BETWEEN SAID SOURCE AND ACCELERATOR, SAID TRAPPING REGION INCLUDING A PINCH-OFF PORTION PROXIMATE SAID SOURCE, A STORAGE PORTION MIDWAY THEREALONG, AND A BARRIER PORTION PROXIMATE SAID ACCELERATOR; MEANS FOR APPLYING A POTENTIAL DISTRIBUTION ALONG SAID TRAPPING REGION WHICH HAS, IN RESPECT TO SAID STORAGE PORTION, A NEGATIVE POTENTIAL DIFFERENCE FROM TION AND A CONTINUALLY INCREASING POTENTIAL DIFFERENCE FROM SAID SOURCE, SAID DISTRIBUTION, RESPECTIVELY, PREVENTING ELECTRONS ENTERING THEREIN FROM ADVANCING AND RETURNING TO SAID ACCELERATOR AND SOURCE, THEREBY FORMING AN ELECTRON BUNCH THEREIN; MEANS TO APPLY A PULSE AT SAID PINCH-OFF PORTION, SAID PULSE ESTABLISHING A NEGATIVE POTENTIAL WITH RESPECT TO SAID SOURCE FOR AN INSTANTANEOUS ISOLATION THEREFROM OF SAID ELECTRON BUNCH; MEANS TO APPLY A NEGATIVE DUMPING PULSE AT SAID STORGE PORTION SUBSEQUENT TO SAID ISOLATION; AND MEANS TO APPLY A POSITIVE PULSE AT SAID BARRIER PORTION SIMULTANEOUSLY WITH SAID DUMPING PULSE THEREBY CHANGING SAID POTENTIAL DISTRIBUTION ALONG SAID TRAPPING REGION TO FORCE SAID ELECTRON BUNCH TOWARD SAID POSTACCELERATOR FOR ACCELERATION THEREFROM PRODUCING A PULSED OUTPUT. 